Electrical rectifier



May 9, 1933. A, .JOFFE 1,907,547

ELECTRICAL RECTIFIER Filed July 2, 1927 A I IgI M I I Patented May 9, 1933 UNITED STATES PATENT OFFICE ABRAHAM J'OFFIE, 0F LENINGRAD, RUSSIA, ASSIGNOR TO INDUSTRIAL RESEARCH COMPANY, OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS ELECTRICAL RECTIFIER Application filed July 2,

The primary object of my invention is to provide an instrumentality for 'efliciently controlling the passage of current through a conductor according to a fixed function of the impressed electromotive force, which function shall provide the properties of detection and rectification. Another object is to devise a combination of elements having these properties, that -is rugged, cheap to manufacture and dependable. Other objects and features will beapparent as the following context is perused in connection with the accompanying drawing.

Fig. 1 shows a rectifying and detecting system; while Fig. 2 illustrates the characteristic curve of my improved device.

The detecting device proper consists of a thin dielectric or poor conducting substance 1 interposed between two metallic electrodes 2-2. The substance may be of any suitable material having low specific conductivity and of requisite thickness, but I prefer to employ a film or coat of linseed oil solidified by baking to high temperature to form a hard, adherent layer or sheet of dimension ranging between 0.2 and 5 Mu (.00002 to .0005 cm) or several such sheets. I have found that with such a sheet when a uniformly increasing potential was applied between electrodes, the increments of current were not proportional to those of the electromotive force but registered first a relatively slow change followed by increases of large amount. The curve 3 depicting this relation has an increasing rate of rise, rapidly rising as the vertical ordinate is ap proached.

If a biasing potential be applied such as to bring the point of operation well down on the knee portion of the curve (point 5 e. g.), equal changes in potential about this point by way of decrement and increment (6 and 7) will result in unequal changes of current (8 and 9) to provide a form of rectification. This potential may be of the order of 1000 volts when the layer has thickness of 0.25 Mu as the thickness is increased within the limits specified. the biasing electromotive force should be increased to several thousand volts. Thus in Fig. 1 I employ the device as a detector of low frequency signals superimposed upon a carrier, the source of biasing potential being indicated at 4. It is apparent that the signal energy undergoes amplification at the time of detection and is rendered distinctly audible in the telephone rece1vers.

Various ways of forming the thin films of dielectric or poorly conducting material are described in my copending Patent No. 1,864,828 which is incorporated herein by reference.

The size of the device, particularly the area of layer 1, and the composition of the material, may be varied widely to produce the desired capacity, and current flow depending upon the frequency of the current to be detected or rectified and other variable factors. For example, for radio use involving a capacity of the order of 0.003 microfarads and asmall current (e. g. 20 microamperes) the area may be as small or smaller than one square centimeter.

I claim:

1-. A rectifier including a solid substance exhibiting a current-voltage characteristic of varying rates of curvature and means for establishing the ope-ration of the substance about a point on the characteristic offering the greatest difference in gradient as measured on opposite sides of said point, said substance comprising a thin layer of solidified linseed oil.

2. Electrical apparatus comprising a circuit containing two electrodes separated by a layer of dimension ranging between 0.2 and 5 Mu as measured in direction of current flow, said layer having low conductivity and a current-voltage characteristic with a curved portion, and means for impressing upon said circuit a current having a unilateral component and an alternating component. the unilateral component having a value at least of the order of a thousand'volts and corresponding to a point intermediate the ends of said curved portion so that alternate half-cycles of said alternating component are localized in sections of said curved portions having different gradients.

3. A rectifying system or the like comprising-two electrodes separated by a thin layer of solid substance of low conductivity, said layer having a dimension ranging between 0.2 and 5 Mu as measured in the direction between the electrodes, and means for impressing a unilateral voltage between said electrodes in the order of 1000 volts, and means for impressing an alternating voltage in series with a load across said electrodes.

4. A rectifier comprising a thin layer of solid substance of a thickness not exceeding about 5 Mu, said layer exhibiting a current voltage characteristic of varying rates of curvature, and means for causing the operation of said rectifier to take place across the smallest dimension of said layer about a point on the characteristic offering a difference in gradient as measured on opposite sides of said point.

5. A rectifier comprising a thin layer of solid substance of a thickness not exceeding about 5 Mu, said layer exhibiting a current voltage characteristic of varying rates of curvature, and means for applying a voltage across the smallest dimension of said layer, producing a high potential gradient through said layer to cause the operation of the rectifier to take place about a point on the characteristic oflering a'diflierence in slope as measured on opposite sides of said point.

Signed by me at Cambridge, Massachusetts, this 7th day of June, 1927.

. ABRAHAM J OFFE. 

